[An early version of this entry said “All but one of these have
been reliably reported as hacker traits (some of them quite often). Even
hackers may have trouble spotting the ringer.” The ringer was
balancing one's checkbook in octal, which I made up out of whole cloth.
Although more respondents picked that one out as fiction than any of the
others, I also received multiple independent reports of its actually
happening, most famously to Grace Hopper while she was working with BINAC
in 1949. —ESR]